Searches for Dark Matter in events with long-lived particles at the LHC

Transcription

1 Marco Schioppa INFN and University of Calabria On behalf of ATLAS, CMS and LHCb Collabora8ons 22/07/17 Searches for Dark Matter in events with long-lived particles at the LHC 1

2 Dark Matter Dark MaDer, 26,8% Dark Energy, 68,3% Ordinary MaDer, 4,9% There is a variety of evidence in favor of the existence of dark mader but only through its gravitafonal influence. Its iden8ty is unknown If DM parfcles are produced at accelerators, we can determine its mass and interacfons LHC is the fronfer probing physics at unexplored energies with unprecedented rates of pp collisions If DM interacts with Standard Model hadrons (e.g. DM scader off nuclei in direct detecfon experiments) then proton colliders will directly produce DM parfcles Many model producing long-lived par8cles (LLP) include DM candidates (produced in associafon with the LLP, mediate interacfons, result from a charged LLP decay) indirect detecfon DM DM direct detecfon SM SM colliders 24/07/17 2

3 candidates from SUSY The currently best mofvated DM candidate in SUSY theory is the lightest superparfcle (LSP) Provides a neutral, weakly interacfng DM candidate 22/07/17 The decay chain can contain parfcles with long lifefme (LLP) if very small coupling in decay chain heavy parfcle mediates the decay no much phase space for decay 3

4 candidates from SUSY Small coupling Neutralino (LLP) Small phase space Chargino (LLP) Heavy mediator Gravi8no (LSP DM candidate) γ Gauge mediated SUSY braking (GMSB) Neutralino (LSP DM candidate) π Anomaly mediated SUSY braking (AMSB); mass of lightest chargino and lightest neutralino are nearly degenerate Electroweakino (LSP DM candidate) 24/07/17 Gluino (LLP) Split SUSY mass of scalars >> mass of fermions R-hadrons 4

5 candidates from hidden sectors/stealth SUSY A scalar boson decays to a pair of prompt hidden sector fermions that in turn decay in long-lived neutral parfcles (the dark photon) and an hidden LSP A pair of gluinos decay to long-lived singlinos, which in turn each decay to a low-mass gravifno and a pair of hadronic jets The π v ± (LSP) are v-charged, but neutral under the SM electrical charge. The π v 0 are the long-lived parfcles that decay to SM quark pairs. 25/07/17 5

6 inelastic Dark Matter (idm) DM could live in a dark sector (DS) with addifonal parfcles and forces. In the idm scenario the heavier parfcles were abundant in the early universe and the coannihilafon of DM with SM was dominant. The current universe would show only the lightest DM states that has no interacfon with SM suppressing indirect and direct detecfon signatures By contrast colliders like LHC can produce both lighter and heavier DM parfcles. In the idm scenario both lighter and heavier DM parfcles are produced simultaneously. When the heavier DM state (excited) decays into the lighter (ground) some SM parfcles are produced indirect detecfon p direct detecfon DM SM DM SM colliders j DM DM* p 23/07/17 6

7 inelastic Dark Matter The characterisfc idm signature is the producfon of DM+DM* in associafon with a hard SM object X, followed by the subsequent decay of DM*->DM+Y : pp -> X +DM+(DM*->DM+Y)=X+Y+missET X is any SM state (jet for hadron machines) that can be used to trigger the event Y is any SM state which nature depends on the mode by which DM couples inelasfcally to the SM. The most promising modes are photon and pair of leptons If DM and DM* are O(100 MeV) O(10 GeV) mass range, the sop SM decay products of DM* are typically aligned with missing momentum The mass spliqng between DM* and DM allows a non-prompt decay of DM* leading to a displaced decay p DM* -> DM + γ, l + l -, j DM DM DM* p γ, l + l - cτ MD* 23/07/17 7

8 Summary LHC machine ATLAS, CMS and LHCb experiments Signatures and results for Heavy stable charged parfcles Disappearing track + MET Photons + MET Displaced jets Lepton Jets Conclusions 22/07/17 8

9 LHC machine In this talk I present results from 3 main detectors: two mulf-purpose detectors and one designed to the study of parfcles with b/c-quark, located 100 m underground ATLAS CMS LHCb LHC is a proton-proton collider at CERN of Geneva s=13 TeV (at present) 40MHz bunch crossing 1232 superconducfng dipole magnet 8.3T max magnefc field 1.9K operafon temperature LHCb CMS ATLAS CERN 22/07/17 9

10 The experiments 22/07/17 JINST 3 (2008) S08004 JINST 3 (2008) S JINST 3 (2008) S08003

11 ATLAS and CMS experiments ATLAS CMS MagneFc field 2T solenoid + toroid (0.5T barrel, 1T endcap 4T solenoid + return yoke Tracker EM calorimeter H calorimeter Si pixel, strips + TRT σ/p T p T Pb + Lar σ/e 10% / E GeV Fe + scint. / Cu + Lar (10λ) σ/e 50% / E GeV Si pixel, strips σ/p T p T PbWO4 crystals σ/e 3% / E GeV Brass + scint. (7λ+catcher) σ/e 100% / E GeV Muon σ/p T 50GeV to 1TeV σ/p T 50GeV to 1TeV (DT/ CSC+Tracker) Trigger L1 + RoI-based HLT (L2+EF) L1 + HLT (L2+L3) VERY FORWARD CALORIMETER MUON CHAMBERS INNER TRACKER CRYSTAL ECAL HCAL 22/07/17 11 Total Weight: t Overall diameter: 14.6 m Overall length: 21.6 m Magne8c field: 4 T SC COIL RETURN YOKE

12 LHCb experiment Single arm forward spectrometer MagneFc field Tracker LHCb Bending power of 4Tm Si strips + straw drip tubes σ/p T p EM calorimeter Pb + sci. pads (25X 0 ) σ/e 10% / E GeV H calorimeter Muon Trigger Fe + scint. (5.6λ) σ/e 69% / E GeV Iron and MWPC L0 + HLT Vertex locator Tracking stafons Calorimeters IP 22/07/17 Muon stafons 12

13 Data taking in Run II During Run II the collected data refers to 13 TeV pp collisions recorded in 2015 and 2016: ATLAS 13.7 (2015) and 24.2 (2016) interacfons per crossing 3.87 (2015) 35.6 (2016) { -1 total recorded luminosity CMS 14 (2015) and 27 (2016) interacfons per crossing 3.81 (2015) 37.8 (2016) { -1 total recorded luminosity LHCb 1.67 (2016) { -1 total recorded luminosity 22/07/17 13 Efficiencies All good for physics close to 96%

14 Search for Heavy Stable Charged Particles in CMS (1/2) CMS PAS EXO Model context: HSCP type hadron like: Pair-producFon of gluino or stop Form R-hadrons (bound state with q or g) HSCP type lepton like: Stau long-lived that decays to gravifno LSP Heavier SUSY parfcles leading to >=1 stau(s) at the end of the decay chain (GMSB benchmark) Direct pair producfon Background: Mainly from instrumental sources R-hadron composed of a spectator HSCP surrounded by cloud of colored, light consftuents (cloud model) Charge-suppressed model CS (almost all R-hadrons flip to neutral) 24/07/17 Different models for strong interacfon of R-hadron with detector material : Event selec8on: Heavy: slow moving -> long TOF to the muon detector Stable (wrt detector): long-lived (τ > 1 ns) Charged: Q >= 1 -> high de/dx in Si tracker 14

15 Search for Heavy Stable Charged Particles in CMS (2/2) CMS PAS EXO tracker-only analysis - require tracks be reconstructed in the silicon detectors tracker+tof analysis - requiring tracks reconstructed in both silicon detectors and muon system Results for Q = 1e Model Analysis Limits gluino (*) Tracker only M > 1590 GeV stop Tracker only M > 1020 GeV stau Tracker+TOF M > 480 GeV (*) How open gluino forms neutral hadron with gluon? f=0.1 considered Results: Data-driven background esfmafon Mass esfmated from de/dx and p Data agrees well with SM background 24/07/17 15 ATLAS limit gluino/sbozom/stop>1580/805/890 GeV with 3.2 s=13tev PLB 760 (2016)

16 Metastable heavy charged particle search in ATLAS Phys.Rev. D (2016) Model context: Split-SUSY and AMSB: NLSP Gluino long-lived Gluino Neutralino (LSP, DM candidate) Background SM processes Overlapping tracks (high ionizafon) Event selec8on: Missing ET > 130 GeV At least one high-pt (150 GeV), isolated, good track Anomalously large energy loss in pixel detector Results No evidence of a signal above the background is observed 24/07/17 16

17 Long-lived chargino search in ATLAS (1/2) Phys.Rev. D (2013) Model context: AMSB: lightest chargino slightly heavier than lightest neutralino (LSP) Chargino predominantly decays to neutralino (missing ET) and sop pion Constrained phase space: chargino long-lived (τ > 0.2ns) Background (mimic disappearing tracks) Charged hadrons interacfng with tracker material Charged leptons losing momenta in tracker due to scadering or bremsstrahlung -> not correctly idenffied 24/07/17 17 Tracks with mis-measured p T

18 Long-lived chargino search in ATLAS (2/2) Phys.Rev. D (2013) Event selec8on: Dedicated trigger to suppress background >= one high-p T jet (ISR-jet), large missing ET, Δφ(jet,MET)>1 One or two disappearing track(s) High-pT, isolated track, missing hits in outer layer of tracker No matching hit in muon detector Small or no calorimeter energy deposit Missing E T (DM candidate) Tanβ is the rafo of Higgs vacuum expectafon values at electroweak scale, Μ is the sign of the higgsino mass term ~2σ excess around 90 GeV. Discrepancy is not consistent with any signal hypothesis studied in this analysis Results: Chargino excluded up to 270 GeV for lifefme=0.2 ns in AMSB scenario 24/07/17 18 CMS limit 260 GeV with 19.5 `-1 data JHEP 01 (2015) 096

19 LLP search in photons+met Qinal state in CMS CMS PAS EXO Model context: GMSB with lightest neutralino is longlived Pair producfon of neutralino -> decay to gravifno (LSP=DM candidate) and photon Consider cτ of neutralino between 0.4 to 100 cm Background: mainly from SM γ+jet Event selec8on: >= 2 high-p T, isolated, good photons (>=1 γ converted in e + e - ) >= 2 jets Missing E T (DM candidate) Results: No excess observed in data Neutralino excluded up to 250 GeV for cτ=10 cm in GMSB (cm) Mean Lifetime cτ χ g g CMS Preliminary g q~ q~ q q ~ χ 1 0 ~ χ ~ G ~ G -1 CMS Conversions Exp. (19.7 fb at 8 TeV) -1 CMS Conversions Obs. (19.7 fb at 8 TeV) -1 CMS Timing Obs. (4.9 fb at 7 TeV) -1 CDF Obs. (2.6 fb at 1.96 TeV) GMSB SPS8 γ E miss T Λ (TeV) χ Mass (GeV) γ 22/07/17 19

20 LLP search in photons+met Qinal state in ATLAS Phys. Rev. D 90, (2014) Model context: GMSB with neutralino is long-lived Pair producfon of neutralino -> decay to gravifno+γ (gravifno=lsp DM candidate) Background: prompt γ, e/jet misidenffied as a γ Event selec8on: Two non-poinfng and delayed photons + MET Results: Data are in good agreement with the background only fit and no evidence for non-poinfng and delayed photons is observed gravifno ATLAS limits stronger than CMS due its LAr ECAL s ability to reconstruct the γ direcfon γ neutralino IP Δz 22/07/17 20

21 Searches for long-lived weakly interacting particle decaying to displaced jets Phy. Rev D 92 (2015) Model context: Stealth-SUSY in which a pair of gluinos decay to long-lived singlinos, which in turn each decay in gravifno (LSP) and a pair of hadronic jets Background: ID fake vertex from jets with high track mulfplicity MS fake vertex Event selec8on: Muon RoI Cluster trigger in a cone ΔR=0.4 with poor acfvity in ID and CAL Require 2 DV (IDVx+MSVx or 2MSVx) Results Limits are set on σxbr of the signal as a funcfon of the singlino proper lifefme 24/07/17 21

22 Searches for LLNP decaying in displaced Lepton-Jets (LJ) ATLAS-CONF Model context: Hidden-Sector (HS) in which a Higgs-like boson decays to HS fermions/scalars that in turn decay in long-lived neutral dark photons (γ D ) decaying to LJ Background SM-mulFjets esfmated with data-driven method cosmics and beam-induced background Event selec8on: Dedicated triggers for displaced objects >= 2 collimated µ without match with ID track or jets with low electro-magnefc energy fracfon (Lepton-Jet=LJ) The search requires 2 LJs in all possible combinafons of e/jets and/or muons Results Limits are set on σxbr of the signal as a funcfon of the proper lifefme of the long-lived parfcle Decay products within ΔR cone <0.5 24/07/17 FRVZ model m H (GeV) Excluded c [mm] Higgs! 2 d + X apple c apple Higgs! 4 d + X apple c apple Higgs! 2 d + X apple c apple 63 Higgs! 4 d + X apple c apple 186 Jets lacks energy deposits in inner layers 22

23 Some other LLP searches (not covered in this talk) LLP pair-produced, decays to ee/ μμ/ eμ displaced di-lepton vertex [CMS PRD 91 (2015) ] [CMS Phys. Rev. LeD. 114 no. 6, (2015) ] [ATLAS Phys. Rev. D 92, (2015)] [ATLAS-CONF ] Search for decays of stopped LLP gluino, stop, sbodom (R-hadron) : Low kinefc energy, come to rest within detector [CMS EPJC 75 (2015) 151] [ATLAS Phys. Rev. D 88, (2013) ] NO Searches for DM with LLP published by LHCb 24/07/17 23

24 Conclusions Both ATLAS and CMS have made great effort to search for DM with LLP Wide range of analyses, looking for many different signatures and open using the detector in interesfng and non-standard ways Various models used for interpretafon. No evidence for new physics so far Limits are put on these new models : best limits Fll now New promising searches are ongoing High expectafon from Run (100/{ expected for ATLAS / CMS): the goal is discovery! 22/07/17 ATLAS Recent results hdps://twiki.cern.ch/twiki/bin/view/atlas/atlasresults CMS Recent results hdp://cms-results.web.cern.ch/cms-results/public-results/ publicafons/ LHCb Recent results hdp://lhcbproject.web.cern.ch/lhcbproject/publicafons/ LHCbProjectPublic/Summary_QEE.html 24